The stored contents of a semiconductor storage device may include data that is undesirable to be read by a third person such as information relating to the privacy of the individual, the information to be protected by a copyright and so on. In order to inhibit the stored contents from being read from the semiconductor storage device without authorization, security circuits have been incorporated in the semiconductor storage devices or peripheral devices for controlling the storage device.
FIG. 7 is a block diagram schematically showing one example of a conventional semiconductor storage device with security circuit. In this prior art, a security circuit SCR is inserted between an interface circuit UI and a semiconductor memory MEM. In reading the semiconductor memory MEM, when an input signal including a read command and a read address is applied to the interface circuit UI, the interface circuit UI analyzes the input signal and transmits the address to the security circuit SCR. The security circuit SCR determines whether or not the transmitted address exists within a memory space that the data is allowed to be read therefrom. If the address is not within the allowed memory space, the security circuit SCR does not apply the read address to the semiconductor memory MEM, and therefore, a normal reading operation cannot be performed. If the address is within the allowed memory space, a correct address is applied from the security circuit SCR to the semiconductor memory MEM. In response thereto, the data is read from the semiconductor memory MEM and outputted to the outside through the interface circuit UI.
The FIG. 7 prior art is a device which intends to protect the stored contents of the semiconductor memory MEM in a manner that when the input address is an address within the allowed memory space, the security circuit SCR does not apply the read address to the semiconductor memory MEM as disclosed in Japanese Patent Application Laying-open No. 59-152599. Furthermore, there is a method involving the read address being disturbed in the security circuit SCR as disclosed in Japanese Patent Application Laying-open No. 63-225839, a method involving the data read from the semiconductor memory MEM being disturbed as disclosed in Japanese Patent Application Laying-open No. 6-250929, and other methods.
A method for removing the security function in the prior art in FIG. 7 is shown in FIG. 8. In FIG. 8, a comparison circuit CMP is utilized. When a password is externally input, the password is input to the comparison circuit CMP. On the other hand, the interface circuit UI fixedly stores a password that is set in advance. The password is also applied from the interface circuit UI to the comparison circuit CMP. The comparison circuit CMP compares the two passwords with each other, and if they are coincident, inputs a security removing signal to the security circuit SCR. Therefore, in this case, the semiconductor memory MEM can be normally accessed, and the normal reading operation can be performed.
In the prior art shown in FIG. 8, in order to control whether or not the security function is to be shown, it is necessary to input the password, and therefore, a security removing method can be easily known by analyzing the input signal. Furthermore, if the semiconductor storage device with security circuit is constructed by a general-purpose ROM chip and a security chip, by removing the ROM chip from a circuit board, it is possible to easily read or copy the data.
Therefore, the illustrative implementations of the present invention are designed to provide a novel semiconductor storage device in which the stored content can be effectively protected from being copied.
The illustrative implementations also provide a semiconductor storage device in which even if the data stored in the ROM is copied, the copied data is made not to be utilized for an original purpose of use.
In accordance with an illustrative implementation, a novel external memory or memory cartridge for a game machine is shown in which an application program or game program can be effectively protected from being copied. The external memory or memory cartridge for a game machine is shown in which even if an application program or game program stored in a ROM is copied, the copied application program or game program is made not to be utilized for its original purpose.
A semiconductor storage according to an exemplary implementation of the present invention is a semiconductor storage device storing regular data and having a security function for preventing unfair use of the regular data, comprising: a first store including a first regular data storing area for fixedly storing first regular data and a dummy data storing area for fixedly storing dummy data; a second store including a second regular data storing area which has a storage capacity equal to at least a storage capacity of the dummy data storing area of the first storing means and fixedly stores second regular data to be originally stored in the dummy data storing area; and a read control mechanism which compares an input address with the dummy data of an address space of the dummy data storing area, to enable reading of the first regular data from the first store when the input address and the dummy address are not identical, and to disable the reading of the first regular data and enable the reading of the second regular data from the second store when the input address and the dummy address are identical.
According to an exemplary implementation of the present invention, even if all the data stored in the first store are read, since further regular data is stored in the second store a part from the first store and the data of the first store includes the dummy data, it is possible to prevent the regular data from being copied as a whole.
More specifically, according to an exemplary implementation of the present invention, the regular data can be normally utilized because the first regular data storing area and the dummy data storing area are formed in the first store, and when the first regular data storing area is accessed, the first regular data is read from the first regular data storing area, and when the dummy data storing area is accessed, the second regular data is read from the second store.
In contrast, even if the stored contents of the first store, i.e. the fist regular data and the dummy data are all unfairly copied without authorization, the dummy data included in the copied data, and therefore, it is impossible to utilize the copied data for the original purpose of use as it is. Therefore, the unfair use can be prevented.
In one implementation of the present invention, the first store includes a masked ROM, and the second store includes a nonvolatile semiconductor memory (a flash memory, for example) which is a writable/readable memory.
The flash memory has a storage capacity larger than a storage capacity of the second regular data storing area, and further includes a dummy address storing area storing the dummy address other than the second regular data storing area, and the dummy address to be applied to the read control mechanism is read from the dummy address storing area.
The flash memory is constructed such that the data is written with a first write voltage in the second regular data storing area and the dummy address storing area, and the data is written with a second write voltage lower than the first write voltage in other areas.
In addition, the flash memory and the read control mechanism is formed within the same single flash memory chip.
In other preferred embodiments, the read control mechanism includes a comparator for comparing the input address and the dummy address with each other to output a first signal or a second signal, an enabling/disabling means for enabling the first storing means in response to the first signal and disabling the first storing means in response to the second signal, and a read address output means for outputting a read address for the second regular data being stored in the second storing means in response to the second signal.
A memory cartridge according to an exemplary implementation of the present invention is a memory cartridge storing an application program and having a security function for preventing unfair use of the application program, comprising: a first storing means including a first program storing area for fixedly storing a first application program and a dummy data storing area for fixedly storing dummy data; a second storing means including a second program storing area which has a storage capacity equal to at least a storage capacity of the dummy data storing area of the first storing means and fixedly stores a second application program to be originally stored in the dummy data storing area; and a read control means which compares an input address with the dummy data of an address space of the dummy data storing area, to enable reading of the first application program from the first storing means when the input address and the dummy address are not identical, and to disable the reading of the first application program and enable the reading of the second application program from the second storing means when the input address and the dummy address are identical.
An electronic equipment according to an exemplary implementation of the present invention is an electronic equipment storing an application program and having a security function for preventing unfair use of the application program, comprising: a first storing means including a first program storing area for fixedly storing a first application program and a dummy data storing area for fixedly storing dummy data; a second storing means including a second program storing area which has a storage capacity equal to at least a storage capacity of the dummy data storing area of the first storing means and fixedly stores a second application program to be originally stored in the dummy data storing area; and a read control means which compares an input address with the dummy data of an address space of the dummy data storing area, to enable reading of the first application program from the first storing means when the input address and the dummy address are not identical, and to disable the reading of the first application program and enable the reading of the second application program from the second storing means when the input address and the dummy address are identical.
A memory cartridge for game machine according to an exemplary implementation of the present invention is a memory cartridge for game machine storing a game program and having a security function for preventing unfair use of the game program, comprising: a first storing means including a first program storing area for fixedly storing a first game program and a dummy data storing area for fixedly storing dummy data; a second storing means including a second program storing area which has a storage capacity equal to at least a storage capacity of the dummy data storing area of the first storing means and fixedly stores a second game program to be originally stored in the dummy data storing area; and a read control means which compares an input address with the dummy data of an address space of the dummy data storing area, to enable reading of the first game program from the first storing means when the input address and the dummy address are not identical, and to disable the reading of the first game program and enable the reading of the second game program from the second storing means when the input address and the dummy address are identical.
In addition, in a case that the second storing means is constructed by an nonvolatile semiconductor memory (a flash memory, for example) and the data is written in the second program storing area with a first write voltage and the data is written with a second write voltage lower than the first write voltage into other areas, in the storing area into which the data is written with the second write voltage, backup data representing the development or progress of the game obtained by executing the first game program and/or the second game program by a processing means of a game machine is written.
In a case that the semiconductor storing device according to an exemplary implementation of the present invention is utilized for a memory cartridge for game machine, if a game main program and/or an important subroutine program is stored in the second game program storing area of the second storing means, unless the second game program is read, it is impossible to execute the game, and therefore, it is possible to implement the copy protect of the game program.
Furthermore, if the second program to be originally stored in the dummy data storing area of the first storing means is stored in the second storing means, and the storage capacity of the second storing means is set to be larger than the storage capacity of the dummy data storing area, by storing data (dummy address) specifying what memory space of the first storing means is the dummy data storing area in the second storing means, the dummy data storing area can be set in an arbitrary memory space of the first storing means. Therefore, it becomes almost impossible to analyze the game program.
Furthermore, in a case that a second storing means further includes a vacant area, if the data that is varied according to the progress or development of the game and necessary for restarting the game after the game is suspended, that is, the backup data such as score point, life, items, player name and etc. is written in the vacant area, it is possible to omit a backup memory which was provided in a conventional cartridge for game machine. That is, the second storing means serves as the second storing means and the backup memory, and therefore, it is possible to reduce the cost.
In addition, if the nonvolatile semiconductor memory is utilized, it becomes unnecessary to provide a backup battery and etc., and therefore, the number of the components can be reduced, and thus, it becomes easy to mount the components on the circuit board.
The above described objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.